Our tests show improvements over 10.8.0, though still not as good as under Lion.

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Apple's release notes for the OS X 10.8.1 update released on Thursday made no mention of widely reported issues with laptop battery life under the initial shipping version of Mountain Lion. However, our testing reveals that the update can indeed significantly improve the runtime of Apple laptops over the original shipping version of Mountain Lion.

That's the good news. The bad news is that battery life may still not be as good as it was under Lion (OS X 10.7.4). And according to scattered reports from readers, the fixes that accompany the update may not fix the situation for everyone.

Shortly after Mountain Lion was released in July, MacBook Pro and MacBook Air users reported seeing significantly less battery life after installing the new OS. Our own initial checks showed that the battery indicator on two different laptops was indeed showing much shorter battery life than we had expected, but the estimated time shown by OS X is still just that—an estimate.

More testing using a Retina MacBook Pro, however, confirmed a 38 percent reduction in battery life simply running Mountain Lion versus Lion. Under Lion, we were able to get consistent 8-hour battery life running our everyday workload. After installing Mountain Lion and running the same software, battery life plummeted to just over 5 hours.

Apple could not confirm any cause for the difference to Ars. However, the company's engineers were reportedly contacting affected customers to collect log data for analysis.

Inexplicable improvement

We immediately began putting those claims to the test after downloading and installing 10.8.1 on Thursday. Indeed, the battery indicator on both my 2010 11" MacBook Air and the 15" Retina MacBook Pro test unit began reporting significantly improved life compared to 10.8.0.

My MacBook Air typically reports between 4.5 and 5 hours on a full charge, while after installing Mountain Lion it would only show about 3.5 hours. After installing the update, it began reporting 4.5 hours consistently. Still, my MacBook Air has seen over two years of constant charge and discharge cycles, and its battery isn't in new condition. I also didn't have any recent runtime tests for comparison.

However, my Retina MacBook Pro had just recently been used to run comparison battery tests under 10.7.4 and 10.8.0. I immediately installed the 10.8.1 update, set up all my usual apps, and disconnected the MagSafe 2 power adapter. The computer ran constantly for 7 hours and 5 minutes before automatically shutting down.

I then charged the Retina MacBook Pro without powering it up; this process will reset the small processor that tracks a MacBook Pro's battery charge status, which can help OS X report more accurate runtime estimates. After fully recharging, rebooting, and making sure all the same apps were running, I again disconnected the power. The Retina MacBook Pro ran for 6 hours and 58 minutes.

Longer bars are better.

That's a significant improvement in runtime, merely from installing a software update. Nonetheless, I still wasn't able to meet the same 8-hour performance I had while running Lion. Similar tests run on a 2011 MacBook Pro by our friends at The Mac Observer showed similar results; battery life improved significantly over 10.8.0, but still fell short of performance under 10.7.4.

We feel confident that battery life should significantly improve for most users who saw problems when running the initial version of Mountain Lion. Still, we have received a number of scattered reports from readers that say their battery problems haven't improved significantly. One user even told Ars that battery life seemed to be worse, so the exact origin of the problem remains unclear.

What is clear from our tests is that whatever fixes Apple added to 10.8.1—whether they were battery-specific or not—resulted in our laptops producing battery life much closer to what we expect. For the time being, though, Apple isn't commenting on the battery issues. Perhaps the company hasn't identified any verifiable contributing factors—there could be more than one single glitch given the range of reported hardware and software configurations of those claiming to have problems.

There's still a chance that further improvements could be coming down the pipeline, though. Apple has already released the first developer preview of OS X 10.8.2, just shortly after pushing out the official 10.8.1 update to the public on Thursday. We haven't heard any reports of additional battery life improvements just yet, but we will definitely continue to monitor the situation.

If you have been able to verify any significant improvement or degradation in battery life after installing 10.8.1, let us know in the comments.